This invention relates to leveling devices; and more particularly to leveling devices having a digital read-out that measure inclination or deviation from the horizontal or vertical.
Leveling devices, commonly referred to as "levels," have been used for many years for multi-varied purposes. Almost all persons engaged in the building industry, whether they be carpenters, brick masons, plumbers, and the like, have a need to use a level during some phase of the construction of the building or other project on which they are working. The most common form of level is the spirit level which utilizes a fluid in a vial or vials to indicate when a desired horizontal or vertical inclination has been reached. Spirit levels offer the advantage of being very simple in construction and operation. They consist merely of a rigid member or body having a straight edge along at least one side thereof. Mounted in this rigid body is a vial having a fluid therein. The fluid is disposed in the vial so as to not quite fill the vial, thereby leaving a bubble or air pocket. The vial, or tube-like member in which the fluid is placed has special markings thereon so that when the vial or tube is exactly horizontal, the indicating bubble will position itself between the markings. Thus, by merely observing the indicating bubble, and by placing the level on the inclination that is to be measured, an indication can be given whether this inclination is "level."
Spirit levels also typically include more than one tube or vial in which the indicating bubble may be observed. One vial or two is typically placed perpendicular to the straight edge of the body of the level, thereby allowing a measure of verticalness to also be made.
Despite the wide use and simplicity of the spirit level, there are problems associated therewith. In particular, spirit levels are of a fixed length. This necessitates that several spirit levels, each of a different length, be accessible to the construction worker who has needs of multi-length levels. Further, in using the spirit level, the indicating bubble appearing in the tube or vial must be visible. Thus, if a builder desires to measure a plane above his eyesight as to whether or not it is level, a builder must climb up on a ladder or similar means in order to look at the bubble in order to find out if, in fact, the desired plane is level. In addition, spirit levels are not very useful for finding or measuring an angle (other than perhaps 45.degree.) that is not level. That is, spirit levels indicate a level condition only. They are not that useful for actually measuring an angle. Moreover, the spirit level is difficult to use as a quasi-transit. That is, builders often have a need to sight along a level line from one location to another in order to find a level point that is some distance from where they are standing. Heretofore, to make such a measurement a transit would have to be set up in order to provide an accurate, level, line-of-sight to the builder. Spirit levels do not lend themselves to providing such a level line-of-sight unless first mounted on a tripod or similar arrangement and held in a level position.
Other types of leveling devices are known in the art. For example, Gooley, U.S. Pat. No. 3,863,067, teaches electronic sensing means to sense the position of the indicating bubble of a spirit-level type device. Wright, U.S. Pat. No. 3,324,564, teaches an electrically responsive level whereby an analog indicator may be coupled with the vial or tube containing the bubble indicator, thereby providing an alternative visual indication of when the level condition is achieved. Higgins, U.S. Pat. No. 3,096,591, discloses a radio frequency leveling device that may remotely indicate a level condition, such as might be used in a missile field.
It is significant to note that all of these prior art devices are used to supplement the basic spirit level device. That is, it appears that all of these devices implement as an element thereof a tube or vial in which a fluid having an indicating bubble is inserted. Furthermore, in order to make the desired leveling measurements, external instrumentation equipment must be used. The use of such equipment not only makes it impractical to use the devices in the building industry, because the leveling devices and equipment are not as portable as a simple spirit level, but also makes the use of the levels impractical because of the expense involved.